DZIURKA Rafał AGH University of Science and Technology

Spoluautoři GÓRECKI Kamil, KOPYŚCIAŃSKI Mateusz, PACYNA Jerzy

The hereby work presents the influence of the retained austenite volume fraction on the phase transformations during tempering. Two different austenitising temperature 830 and 1050 °C were selected. For each austenitising temperature two samples were hardened in dilatometer. One sample immediately after hardening was tempered in dilatometer the other before tempering was cooled in liquid nitrogen for 1 h. The investigations of phase transformations during tempering of the steel were made on the ground of dilatometric curves recorded during heating from as-quenched state. Dilatometric investigations were performed by use of the DT 1000 dilatometer made by Adamel, and L78 R.I.T.A. (Rapid Intensive Thermal Analysis) dilatometer made by Linseis. The methodology of the dilatometric investigation and the method of the characteristic points determination were described. The microstructure analyses were performed using FEI Nova NanoSEM 450 and light microscopy made by Zeiss. The effect of austenitising temperature and sub-zero treatment on the retained austenite volume fraction was studied. During tempering the amount of retained austenite can significantly affect the final properties of the steel. High volume fraction of retained austenite may increase temper brittleness effect caused by the creation of a large amount of fresh martensite, therefore its stability problem is very important.